The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Known powertrain architectures include torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Electric machines, operative as motors or generators, generate an input torque to the transmission, independently of an input torque from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating range state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed.
The transmission enables transitions between a plurality of operating range states. The transition from one operating range state to another operating range state may involve transitioning at least one clutch state. The clutch state can include an ON state indicative of the clutch being activated and engaged and an OFF state indicative of the clutch being deactivated and disengaged. Transitions between clutch states include control measures to reduce or eliminate an occurrence of clutch slip during transitions between clutch states. Clutches, in order to avoid slip, remain engaged with a minimum clutch torque capacity whenever a reactive load is transmitted through the clutch. Clutch torque capacity is a function of hydraulic pressure applied to the clutch. Thus, greater hydraulic pressure in the clutch results in a greater clamping force within the clutch and a resulting higher clutch torque capacity. Accordingly, a hydraulic control system utilizes lines charged with hydraulic oil to selectively activate and engage clutches within the transmission.
It is known to control line pressure for achieving a required torque capacity in a clutch based solely on a current estimated clutch load in a reactive manner that can result in increased response times which are undesirable. Generally, increases in the load applied to the clutch are limited by how quickly the clutch capacity is increased in response to small iterative changes to the estimated clutch load, which are ultimately driven by changes in an operator torque request. Such increased response times are undesirable because the reactive load applied to the clutch must wait for a change in the operator torque request. Additionally, torque capacity in some instances needs to be increased despite no change in the operator torque request. This can result in hydraulic line pressure being inadequate, resulting in clutch slippage and decreased drivability.
It is further known to implement crude logic which creates “headroom” for possible upcoming increases in reactive load applied to a clutch by increasing the line pressure applied to the clutch by a predetermined margin. However, increasing the clutch load by the predetermined margin alone requires a trade-off between having a margin that is large enough to allow for a sufficient response, and a margin that is minimized to minimize hydraulic pumping losses. Thus, maintaining the predetermined margin of line pressure applied to the clutch may result in increased response times and decreased fuel economy.